Leucine-rich repeat containing G protein-coupled receptor (LGR5) is a part of the WNT/&beta;-Catenin signaling pathway, responsible for intestinal stem cell maintenance. These Lgr5-2A-EGFP-2A-CreERT2 knock-in (KI) mice express enhanced green fluorescent protein (EGFP) and an iCre/ERT2 fusion protein from the Lgr5 promoter/enhancer elements. As the P2AEGFP-T2A-CreERT2 sequences were inserted into the 5'end of the endogenous stop codon, endogenous Lgr5 expression is retained. Homozygous Lgr5-2A-EGFP-2A-CreERT2 KI mice are viable and fertile with no overt phenotype. EGFP fluorescence is observed in crypt base columnar cells in small intestine (aka stem cells of the small intestine) and colon. iCre-ERT2 fusion gene activity is observed in the same cells following tamoxifen administration. The donating laboratory indicates that fluorescence is detectable by flow cytometry and by immunohistochemistry/immunofluorescence. The iCre-ERT2 fusion protein consists of an iCre recombinase fused to a triple mutant form of the human estrogen receptor, which does not bind its natural ligand (17&beta;-estradiol) at physiological concentrations but will bind the synthetic estrogen receptor ligands 4-hydroxytamoxifen (OHT or tamoxifen) and, with lesser sensitivity, ICI 182780. Restricted to the cytoplasm, iCre-ERT2 can only gain access to the nuclear compartment after exposure to tamoxifen. To counteract the mixed estrogen agonist effects of tamoxifen injections, which can result in late fetal abortions in pregnant mice, progesterone may be co-administered. As such, when Lgr5-2A-EGFP-2A-CreERT2 KI mice are bred with mice containing loxP-flanked sequence of interest, tamoxifen-inducible, Cre-mediated recombination will result in deletion of the floxed sequences in the Lgr5-expressing cells of the offspring.

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Lgr5-2A-EGFP-2A-CreERT2 knock-in mice express an enhanced green fluorescent protein (EGFP) and an iCreERT2 fusion protein driven by the Lgr5 endogenous promoter. Endogenous Lgr5 expression is retained. When these mice are bred with mice containing a loxP-flanked sequence of interest, tamoxifen-inducible, Cre-mediated recombination will result in deletion of the floxed sequences in the Lgr5-expressing cells of the offspring. These mice may be useful for lineage-tracing or marking Lgr5-expressing stem cells of the small intestine.

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